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Twentieth-century fire exclusion has produced unnatural and undesirable changes in vegetation structure and dynamics of many rangelands of western North America, but not all kinds of ecosystems have been so affected. A comparison of the historical and modern fire regimes, especially in peripheral populations that can be particularly vulnerable to climatic change, can help guide fire management planning with information on the degree to which a local area has been altered by past fire exclusion. Historical fire rotations in piñon-juniper ( Pinus edlis Engelm. -Juniperus spp. L.) woodlands vary widely across woodland types, hence management applications should be specific to local historical and modern fire characteristics. We asked if the modern fire rotation is similar to or longer than the historical fire rotation before arrival of Euro-American settlers on the northern woodland boundary in northwestern Colorado and northeastern Utah. This study was initiated by managers from Dinosaur National Monument (DINO) concerned that lack of 20th-century fire may have allowed unnatural expansion of piñon-juniper woodlands into grasslands and shrublands. Fire history analysis using dendrochronology methods suggests a historical (pre-1900) fire rotation of ca. 550 yr, comparable with or longer than many other woodlands on the Colorado Plateau. In contrast, analysis of digital fire records reveals that the fire rotation between 1981 and 2010 was substantially shorter than historical; if only natural fires are considered, the piñon-juniper fire rotation was 364 yr, and if anthropogenic fires were included, the fire rotation was 233 yr. This shorter fire rotation supports a previously documented contraction in woodland extent in DINO during the past 90 yr. Our data support reducing the amount of fire in the landscape to preserve the integrity of the natural vegetation of this and other piñon-juniper woodlands, especially under projections of warmer and drier future climates.

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